Guide bushing offset chart & calculator
The offset is how far the cut lands from the template edge. It is the same on every side and every curve, and it's set by two numbers: the outside diameter of your guide bushing and the diameter of your bit.
Worked examples
- 5/8" bushing, 1/4" bit: (0.625 − 0.25) ÷ 2 = 3/16"
- 1/2" bushing, 1/4" bit: (0.5 − 0.25) ÷ 2 = 1/8"
- 3/4" bushing, 1/2" bit: (0.75 − 0.5) ÷ 2 = 1/8"
- 7/16" bushing, 1/4" bit: (0.4375 − 0.25) ÷ 2 = 3/32"
- 5/16" bushing, 1/8" bit: (0.3125 − 0.125) ÷ 2 = 3/32"
Don't want to do the math? Rideline calculates it and applies it to your shape for you.
Inch offset chart
| Bushing OD ↓ / Bit → | 1/8" | 3/16" | 1/4" | 3/8" | 1/2" |
|---|---|---|---|---|---|
| 5/16" | 3/32" (0.0938") | 1/16" (0.0625") | – | – | – |
| 3/8" | 1/8" (0.1250") | 3/32" (0.0938") | 1/16" (0.0625") | – | – |
| 7/16" | 5/32" (0.1562") | 1/8" (0.1250") | 3/32" (0.0938") | – | – |
| 1/2" | 3/16" (0.1875") | 5/32" (0.1562") | 1/8" (0.1250") | 1/16" (0.0625") | – |
| 5/8" | 1/4" (0.2500") | 7/32" (0.2188") | 3/16" (0.1875") | 1/8" (0.1250") | 1/16" (0.0625") |
| 3/4" | 5/16" (0.3125") | 9/32" (0.2812") | 1/4" (0.2500") | 3/16" (0.1875") | 1/8" (0.1250") |
| 1" | 7/16" (0.4375") | 13/32" (0.4062") | 3/8" (0.3750") | 5/16" (0.3125") | 1/4" (0.2500") |
Metric offset chart
| Bushing OD ↓ / Bit → | 3 mm | 4 mm | 6 mm | 8 mm | 10 mm | 12 mm |
|---|---|---|---|---|---|---|
| 10 mm | 3.5 mm | 3 mm | 2 mm | – | – | – |
| 12 mm | 4.5 mm | 4 mm | 3 mm | 2 mm | – | – |
| 13 mm | 5 mm | 4.5 mm | 3.5 mm | 2.5 mm | 1.5 mm | – |
| 17 mm | 7 mm | 6.5 mm | 5.5 mm | 4.5 mm | 3.5 mm | 2.5 mm |
| 24 mm | 10.5 mm | 10 mm | 9 mm | 8 mm | 7 mm | 6 mm |
| 27 mm | 12 mm | 11.5 mm | 10.5 mm | 9.5 mm | 8.5 mm | 7.5 mm |
| 30 mm | 13.5 mm | 13 mm | 12 mm | 11 mm | 10 mm | 9 mm |
Which way does the offset go?
- Bushing inside the template (pockets, recesses, openings): make the template opening larger than the finished pocket by the offset on every side. A 3" circle pocket with a 3/16" offset needs a 3-3/8" opening.
- Bushing outside the template (cut-out parts): make the template smaller than the finished part by the offset on every side. A 3" circle part with a 3/16" offset needs a 2-5/8" template.
Why you can't just scale the shape
Scaling a drawing up by a percentage moves every edge by a different amount: long edges move more than short ones and the centre doesn't move at all. An offset moves every edge by exactly the same distance, the way a bushing actually rides. Except for circles, scaling gives you a template that cuts the wrong shape. Use a true offset (Inkscape's Path ▸ Linked Offset, Illustrator's Offset Path, or Rideline).
Check your real bushing size
Bushings are sold by nominal size, and some brands are close to but not exactly their marked size. A few thousandths matter for inlays. Measure the collar with calipers and type the measured value into Rideline's custom field. Also check that the bushing is centred in the base plate. A centring cone or pin helps, and an off-centre bushing shifts the cut toward one side.
Collar length matters too: the template has to be thicker than the collar is tall, or the collar will hit the workpiece. Most templates are 1/4" (6 mm) thick for this reason.